This invention relates to an improved process for making cement, more particularly to an improved process for producing Portland cement clinker for use in the production of cement. In one aspect, the present invention relates to an improved process for making Portland cement clinker using substantially dry, naturally recovered, unprocessed aragonite as the calcareous material employed to produce Portland cement clinker. In yet another aspect, the invention relates to an improved method for producing Portland cement clinker employing substantially dry, naturally recovered, unprocessed aragonite as the calcareous reactant material and a substantially dry argillaceous material, wherein the argillaceous material is selected from the group consisting of clay, kaolin, shale, slag, fly ash and mixtures of same.
Portland cement has heretofore been made by intergrinding combinations of calcareous materials such as calcitic limestone, oyster shell, aragonite, and an argillaceous material, such as clay, shale, slag, fly ash and other reactant materials such as silica sand. These pulverized materials are carefully blended by one of many methods and the blend or mix is then fed dry or as an aqueous slurry into a rotary kiln. Much work and energy is expended to establish the important physical and chemical parameters of the raw kiln feed prior to introducing them into a rotary kiln. Typically about one-third of the total electrical energy required to manufacture Portland cement is expended in the initial blending and grinding of the raw feed constituents. The kiln burns or reacts these materials at temperatures around 2700.degree. F to form Portland cement clinker. As the clinker exits from the kiln, it can be quenched, if desired, for example, by a stream of air or steam or by immersion in water. The clinker so formed is then interground with predetermined amounts of calcium sulfate or other set controlling agents ground to a finely divided powder. In addition to calcium sulfate or other set controlling agents, this powder is composed of compounds of lime, alumina, silica and iron oxide as tetracalciumaluminoferrite, tricalciumaluminate, tricalciumsilicate and dicalciumsilicate. Small amounts of other materials such as magnesia, sodium, potassium and sulfur and other trace elements are also present in the combined form. The powder thus formed is generally known as Portland cement, and has the property of hardening slowly when mixed into a paste with water. The set time of Portland cement can be controlled by varying the amount of calcium sulfate or other set controlling agents.
In the production of cement from such prior art processes, it has generally been the practice to finely grind the reactant material and thoroughly blend it before being fed to a kiln for burning. Such materials can be ground and blended by either dry or wet grinding methods.
Recently, new methods of producing cement wherein aragonite is employed as the calcarceous component have been set forth. Typical of such processes is that disclosed in U.S. Pat. No. 3,686,372, entitled "Method For Making Cement" wherein aragonite is disclosed as the calcareous component of the reactant mixture for the production of Portland cement. When using the process of the before mentioned patent, aragonite can be ground to a lesser fineness than required for conventional calcareous materials, such as limestone or oyster shells, or the aragonite can be screened to remove coarse particles, so that the recovered finer particles can be used without grinding. However, this process employs conventional grinding and blending methods. Thus, heretofore, when employing aragonite as the calcareous material, expense has been incurred in the grinding and blending of the aragonite, even though the aragonite is normally ground to a lesser degree of fineness than the previously known calcareous materials and/or additional separating steps are employed for removing coarse aragonite particles. The grinding operation and the screening or other appropriate methods for removing the coarse aragonite as well as the blending of said aragonite with the argillaceous portion of the mix are time consuming and expensive. It is therefore desirable to reduce, and if possible, eliminate the costs of grinding and separating fractions as well as the blending of the calcareous component of the reaction mixture for the production of cement clinker, even when using aragonite as such materials. Such would significantly reduce the power requirements for processing of the calcareous component and would eliminate the capital investment and operating expense required for grinding equipment, screens, sieves and other separating equipment and shakers, as well as for blending, storage and transporting.